1. Field of the Invention
The present invention relates to an intake structure for an internal combustion engine for preventing a filter of an air cleaner from being contaminated by a fuel contained in a blowback flow from an internal combustion engine.
2. Description of the Related Art
Internal combustion engines, in particular, piston valve-type two-cycle internal combustion engines have a characteristic in that a large amount of blowback of a fuel from a cylinder through a carburetor toward an air cleaner occurs. When fuel particles reach a filter of the air cleaner due to the blowback, the filter is clogged. As a result, an engine output is lowered. Thus, in order to block the blowback of the fuel toward the air cleaner, an anti-blowback member is provided so as to face an inlet of the carburetor. Conventionally, the anti-blowback members having various structures have been proposed (see, for example, Japanese Utility Model Application Laid-open No. Sho 60-100560 and Japanese Patent Nos. 3727249 and 2514621).
In general, the anti-blowback member is required to have an excellent blowback blocking effect for reliably blocking the blowback of the fuel from the inlet of the carburetor, whereas good fresh-air induction efficiency is required during an intake stroke of the internal combustion engine. In order to meet the requirements described above, various measures have been taken thus far. If a configuration is complex, however, there arises a problem in costs. On the other hand, if a size is increased, there arises a problem in that the requirement for downsizing of a product or components is not satisfied. In particular, for portable operating machines including the internal combustion engine as a driving source, there are strong needs for downsizing and light-weighting of a machine body. Thus, the air cleaner including the anti-blowback member is preferably formed as compact as possible.